The present invention relates to a variable speed drive of the oil shear type and which is particularly suited for transmitting torque at a variable speed from a prime mover such as an electric motor to a driven apparatus such as a pump, mixer, sewage aerator or the like. For such applications, it is common to mount an electric motor on top of a variable speed drive having a depending output shaft. The vertical shaft of the motor is coupled to the vertical input shaft of the variable speed drive, and the coaxial output shaft of the drive is coupled to the vertical shaft of the pump, mixer or other device to be driven. Preferably, a series of clutch discs are mounted on the input shaft and interfit with a series of clutch plates which are connected to rotate with the output shaft. A supply of oil is pumped or forced between the interfitting clutch discs and plates to maintain an oil film therebetween and to remove heat therefrom. The clutch discs and plates are clamped together by actuation of a piston which usually rotates with the output shaft.
One form of an oil shear variable speed drive which has been manufactured and sold by the assignee of the present invention, is disclosed in abandoned U.S. patent application Ser. No. 690,124, filed Dec. 13, 1967. This variable speed drive is constructed and installed so that the common axis of the input shaft and the output shaft is horizontal, and the oil which is forced or pumped between the clutch discs and plates is collected within the bottom of the housing which may incorporate a heat exchanger.
In a vertical type variable speed drive, the housing is constructed so that the oil flowing outwardly between the clutch disc and plates, is collected within a chamber defined within the lower end portion of the housing or within an external reservoir tank. It has been found highly desirable for the reservoir chamber to hold a substantial volume of oil, particularly with variable speed drives used for transmitting hundreds of horsepower, in order to provide for a high flow rate of oil outwardly between the clutch plates and discs. This high flow rate assures continuous lubrication of the plates and discs and also removes the substantial heat developed, especially when the output shaft is driven at a lower speed than the input shaft and relative slip occurs between the clutch plates and discs.
When the oil reservoir chamber is located within the lower portion of the housing of a vertical variable speed drive, the output shaft of the drive must be constructed with substantial length so that the clutch plates and discs are rotated at an elevation above the maximum level of the oil within the reservoir chamber. As a result, the housing for the variable speed drive must be constructed with a substantial vertical height, thereby elevating the location of the drive motor and increasing the overall stack height of the motor and variable speed drive assembly. This increase in length or vertical height of the output shaft also results in increasing the problem of vibration of the output shaft which must be precisely balanced to provide for long dependable service.